Ilia V. Baskakov, PhD

https://scholar.google.com/citations?user=IbYW5mkAAAAJ&hl=en&oi=ao

Our laboratory use animal pathology, transcriptome analysis, neuroimmunology and cell biology along with structural, biochemical and imaging approaches to gain new knowledge on prion-induced neurodegeneration.  Prion diseases, or transmissible spongiform encephalopathies, are fatal neurodegenerative disorders that can arise spontaneously, be inherited or acquired through transmission. The transmissible agent of prion diseases devoid of nucleic acids, but instead consists of a prion protein in its abnormal, β-sheet rich state (PrP^Sc), which is capable of replicating itself according to the template-assisted mechanism.

Evolution of prion strains and deformed templating. In a series of studies conducted over 15 years, we introduced a new concept that transmissible prion diseases can be induced in wild type animals by PrP structures with a folding pattern fundamentally different from that of authentic prions or PrP^Sc. These studies provided compelling evidence that noninfectious amyloids with a structure different from that of PrP^Sc could lead to transmissible prion disease via a mechanism referred to as deformed templating. Moreover, using new imaging approach developed by my laboratory that combines atomic force and fluorescence microscopy, we showed for the first time that, indeed, a folding pattern can switch from one cross-b pattern to an alternative cross-b pattern within individual amyloid fibrils. This work provided important insights into the genesis of the transmissible protein states and has numerous implications for understanding the etiology of neurodegenerative diseases in general.

Establishing a causative relationship between prion strain-specific structure and disease phenotype. While existence of multiple prion strains have been well established, the question how individual strains elicit multiple disease phenotypes is one of the most puzzling in prion and other neurodegenerative diseases. Prion protein is posttranslationally modified with two sialylated N-linked glycans. We showed that among hundreds of PrP^C sialoglycoforms expressed by a cell, individual prion strains selectively recruit those PrP^C sialoglycoforms that can be accommodated within a strain-specific structure. We illustrated that strain-specific patterns of carbohydrate groups are formed on a surface of PrP^Sc particles that dictate a strength of proinflammatory response of microglia. Since posttranslational modifications are common among proteins implicated in neurodegenerative diseases (tau, a-synuclein), the novel mechanism on strain-specific selective recruitment described in our work has broad implication beyond the prion diseases.

Role of prion protein sialylation determining prion fate in an organism. Through appreciation of the roles sialylation plays in biology, our recent studies put forward key evidence illustrating that sialylation of N-glycans of prion protein is essential for understanding prion biology. We demonstrated that sialylation of PrP^Sc N-linked glycans controls prion fate in organisms, dictates neuroinflammation status and the outcomes of prion infection. In particular, we showed that challenge of a host with PrP^Sc with reduced sialylation levels does not cause prion infection or prion disease. Moreover, prion infectivity could be switched off and on reversibly via removing and reinstalling PrP^Sc sialylation. Removing PrP^Sc sialylation was found to abolish prion lymphotropism, i.e. selective trafficking of prions to secondary lymphoid organs that are known to be the first sites of prion replication upon peripheral challenge.

Role of microglia in pathogenesis of prion diseases. Discovering the relationship between PrP^Sc sialylation status and neuroinflammation led to the next quest as to whether neuroinflammation drives disease progression. Toward this question, transcriptome analysis of 17 animal groups revealed very strong inverse correlation between the degree of neuroinflammation and the incubation time to diseases suggesting that phenotypic changes in glia contribute to faster progression of diseases and, perhaps, even drive the disease pathogenesis Transcriptome analysis revealed that with the disease progression, the region-specific microglial homeostatic signatures were replaced by the region-independent neuroinflammation signature characterized by significant upregulation in microglial phagocytic pathways. Consistent with gene expression analysis, reactive microglia isolated from prion-infected mice showed dramatic increase in phagocytic uptake of both disease-associated and normal synaptosomes. The current projects in the lab examine the role of microglia-driven phagocytosis in prion disease pathogenesis.  In particular, we are interested whether phagocytic activity should be targeted as a potential therapeutic strategy for treating prion diseases.

Defining the role of reactive astrocytes in pathogenesis of prion diseases. Our recent studies found that astrocytes responded to prion infection earlier than microglia. Region-specific transcriptome analysis revealed a global dysregulation across multiple homeostatic functions including loss in neuronal support in reactive astrocyte. Moreover, we observed very strong inverse correlation between the degree of astrocyte reactivity and the incubation time to diseases suggesting that phenotypic changes in astrocytes contribute to faster progression of diseases and, perhaps, even drive the disease pathogenesis. In support of this hypothesis, reactive astrocytes isolated from prion-infected mice had deleterious effects on primary neurons. The current projects in the lab seek to establish the role of reactive astrocyte in prion diseaseas and test whether transformation of astrocytes into reactive states drives pathogenesis of the disease.

Our laboratory use animal pathology, transcriptome analysis, neuroimmunology and cell biology along with structural, biochemical and imaging approaches to gain new knowledge on prion-induced neurodegeneration.  Our laboratory is equipped with Atomic Force Microscope PicoLE combined with the inverted fluorescence microscop, CD spectrophotometer J- 810 (Jacso); FTIR spectrometer Tensor 27 equipped (Bruker); fluorimeter FlouroMax-3 (Jobin Yvon); dynamic light scattering DynaPro-MS/X (Protein Solutions); HPLC system with fluorescence and photodiode detectors (Shimadzu); FPLC system Akta prime (Amersham); fluorescence inverted microscope TE-2000 (Nikon); automated sonicators Misonix S-4000.

Lab Members

Natallia Makarava, B.S., Research Associate
Rajesh Kushwaha, Ph.D., Postdoctoral Fellow
Olga Bocharova, Ph.D., Postdoctoral Fellow
Kara Molesworth, B.S., Animal Specialist
Olga Mychko, B.S., Laboratory Technician
Narayan Pandit, M.S., Laboratory Technician